So I brought a worked A15 a few months ago,
Its had a few mods, blue printed,balanced,skimmed,mild cam etc. Its running a single down draught A12 carb thats been been bored out and heavily modified by an oldschool datsun guru engine builder.
When I first looked inside the rocker cover it had alot of white'ish whipped cream looking oil through it.
At that stage it was just thought to be condensation (hopefully) so it was cleaned out and had an oil flush treatment and oil and filter change.
The build up of gunk was back in no time at all.
I then found about 5-10ml of water in the breather hose when i pulled it off the bottom of the air cleaner breather port. I got rid of that water and gave it another oil change but after about three hours driving when I checked the breather hose again the water was back and so was the gunk in the rocker cover.
I will try and explain the breather setup on it as its a little different than standard:
Ok so picture the breather hose coming up from back of block (off the metal pipe fitting that comes off the side of the block) and up to jst above height of rocker cover then arching down onto the rocker cover breather port.
Roughly at half way up that hose, as you view it in the eng bay, there is a "T" joiner.
Then hose comes off the "T" slightly curves down and then back up to the air cleaner hsg breather port (its a standard air cleaner hsg), - in the low point of that curve between the "T" and the air cleaner is where the water has been building.

There is no sign of the thick white oil on the dip stick min-max area, but there is a tiny amount around the top of the dip stick seal near the handle.

The radiator seems to keep an even level, Ive only topped it up a small amount (3/4 cup) maybe 2 times in as many months.

So, ahhh.., yea.. any thoughts as to the why and how would be greatly appreciated.
Is it just a symptom of having a modified carb?

Cheers

Water in the oil will manifest itself as milky oil, as evidenced on the dipstick. If instead you are only seeing water/oil mixture on the underside of the oil cap, that is a condensation problem, but not water 'in' the oil.

What causes this? poor ventilation OR engine not getting hot enough (less than 160F degrees) OR short, small driving trips (less than 15 minutes at a time). The engine needs to be hot enough to burn off the natural water condensation that occurs.

A modified carburetor does not normally cause this. Water doesn't run through the carburetor, neither does the crankcase breather except at wide open throttle.

Your breather setup sounds like a fairly typical "shade tree" or "backyard" solution, I've seen it done before. I would refit the stock breather system as it won't hurt HP, but will ensure effective crankcase breathing. An old wives tale is that it will hurt performance, but that it untrue. Guys that say that always point to pet theories, but never to any testing either dyno testing or otherwise. Refit the PCV so that the crankcase is positively aired out.

Only if you are racing and the racing rules require a catch can -- only then should the PCV system not be used.

Thanks,
I will re-fit the factory PCV then.

"" If instead you are only seeing water/oil mixture on the underside of the oil cap, that is a condensation problem,""

Its not just on the cap, its more like a half cup right through the valve train and underside of the rocker cover.
It doesnt really get taken on small trips. At the mo its running a A12 radiator till i get the N14 one that i have all set-up. The A12 rad seems to be working ok in the mean time, Ive fitted a (pricey) after market water temp set-up in the top rad hose and the gauge stays around 74 degrees and has never gone over 78.

I was thinking of fitting an after market air cleaner at some stage, in that case I would have to move to a catch tank system- would that be prone to the same condensation probs im getting now?

Thanks again

Nice temps. It seems you do not need a larger radiator as the temp is already rock steady.

You can use the stock breather system with aftermarket air cleaners. Just fit the rocker breather hose to the aftermarket cleaner lid.

Yeah thats what i originally thought in regards to the radiator though Ive since heard stories of A15 engines cooking while running 12 radiators despite what the water temp reading is.
..I dunno, im kinda at odds about it.

-And yeah true that re the after mkt air cleaner, I jst didnt think of it ;)

Cheers man, keep up the good work

dd is on the money. It's condensation from blow by gasses. Re-fit the PCV valve to the bottom side of the carby, plumb that to the block line and vent the rocker line to the air cleaner or fit it with a filter (air goes in at the rocker cover). All the deets are in the tech wiki.

You'll also see this with clapped out engines since the excessive blowby prevents effective venting but even then it clears up with a long drive, longer the better.

If the temp is good, the A15 will not cook. It takes 100C or more to cook an A15. Although the important temp is the coolant in the cylinder head. The temp in the upper radiator hose is less important.

Good point LD. To check for excessive blowby, see http://datsun1200.com/modules/mediawi ... =Smoke_Tests#Blow-by_Test